Social bookmarking takes an overwhelming role in the current Web 2.0 arena. It enables knowledge sharing and efficient discovery on the web, where different users can collaborate together by tagging documents of interest.
By allowing users the freedom to choose their own vocabulary to describe documents via annotations (tags), a social bookmarking system offers a highly flexible solution compared to traditional annotation systems which were restricted in their vocabulary usage. For these reasons, social bookmarking systems have become highly popular as means for users to organize and share their bookmarks with others.
Attention has been given to utilizing social bookmarking data to enhance traditional information retrieval (IR) tasks. For that purpose, traditional document-centric models have been extended to consider also new entity types such as the users of the system and the tags associated with the system's documents, in order to capture the different relationships between documents, users, and tags, which are embedded in bookmarks.
The social entities of a bookmarking system (i.e., documents, users, and tags) are commonly considered independently, where each entity is considered as a fundamental element of the system. Therefore, solutions to different tasks that utilize social information neglect the fact that each bookmark may imprint a unique entity on its own, which if considered, could contribute to improving those specific tasks.
As an illustrating example, the tag “bob” is considered that is associated with 155 different Web pages in an example bookmarking system. A simple analysis of these bookmarks reveals that many of the users who gave that tag are named “Bob” (or Robert) while only a few used that tag for the page titled “Blue Opportunity Bank (BoB)”. While a user named “Bob” is welcome to tag any document with his name, it is easy to see that such bookmarks do not provide much benefit for IR tasks and might even mislead. Therefore, the set of bookmarks sharing the tag “bob” should be split into useful bookmarks (e.g., those associated with the “BoB” page) and private ones with much less benefit. The former are termed community tags (i.e., tags which can be used by the community) and the latter, private tags.